Doubling smaller dock lines equal to next size line?

Discussion in 'Powerboats' started by sdowney717, Oct 18, 2021.

  1. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Right now, I use 5/8" to mostly 3/4" 3 strand nylon dock lines on my 37 foot boat.
    But I was wondering if using 1/2" double braided doubled up to a cleat is about the same as using the larger 5/8" line.
    I have worn out dock lines before especially around pilings and cleats, (none have broken yet in 20 years regarding the boat ) so would using 2 dock lines of a smaller diameter be safer against a single dock line of larger diameter breaking?

    I know double braid is stronger the 3 strand nylon for the same size.
     
  2. Will Gilmore
    Joined: Aug 2017
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    Location: Littleton, nh

    Will Gilmore Senior Member

    Yes and no.
    For dock lines, it is not all about strength. It is also about stretch. Different docking situations require more or less attention to stretch in the lines.

    In general, stern and bow lines are left loose, but at the limits that prevent the boat from banging into the pilings, pier, neighbor's boat or other objects. Spring lines keep the boat from moving forward and backwards. When there is no tidal change, such as on a lake or a floating dock, that's all you have to worry about. Stretch in the lines will aid in reducing shock forces on cleats and other connected parts of a boat and the dock.

    When you have to deal with a tidal range, stretch becomes even more important for keeping the boat in her position while allowing her movement up and down with the tide. Spring lines do more of the work and efforts to lengthen stern and bow lines are taken, such as crossing a port line to the starboard cleat or replacing bow lines with a bow spring line, bringing them aft to give them length.

    Three strand rope has natural mechanical stretch built in. Double braid is less stretchy, but there are some, such as climbing rope, that have stretch designed into them to reduce the shock on a falling climber.

    Assess your docking needs and consider what they might be if you sail to another port and tie up temporarily. If you're lake sailing, no problem. If there are tides where you sail and one marina might have a floating dock, but another doesn't, take those things into account.

    You can also add a little extra stretchiness by twisting your doubled-up lines together, the more turns the more stretch.
     
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  3. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    Of course I am tidal and on a fixed dock, Chisman Creek off the Chesapeake bay, and have always used 3 strand nylon dock lines. I recently got some very good deals on new dock lines to cut up for new fender lines, but was wondering about using them as dock lines too, so then the idea of doubling up double braid came to mind. Maybe half the boats here at the marina use smaller double braided lines. I am one of the larger boats at 37 feet, my slipmate has a 28 foot Tiara with 1/2" double braid doubled up and he seems ok now for years. A few boats have broken their lines but their owners also dont care to visit their boats often. A larger 40 foot Luhrs uses either 5/8 or 3/4 double braid for years. But I have noticed some of those lines have worn thru the outer black cover.
     
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Doubling up lines doesn't usually double strength. If they aren't exactly the same length, one will take 100% of the load until it fails then the other will get the load.
     
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  5. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    yes, I think though it is progressive loading as lines stretch, not absolute like a metal chain depending on how well you tie the lines, and they do say to double your lines if a bad storm is coming, I dont have a plan to do this, but was just thinking on it. I dont mind changing all dock lines to double braid 5/8.
     
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  6. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    One anti-chaff measure I have used is to tie off the dock line to a short chain wrapped around a piling.
     
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  7. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I use 2.0" lay-flat hose as anti-chafe gear. It stores well, is dirt cheap, and can be slid over anything. You can punch a hole in it and tie an idiot cord to it to hold it in place relative to cleats and pilings.

    Nylon 8 ply braided dock lines are very nice. I get the black ones for better UV. But they cost about double 3 strand.
     
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